We have identified a novel heparin-like peptidyl coagulation inhibitor that is a peptide fragment of a naturally-occurring human fibrinogen isoform, gammaA/gamma' fibrinogen. The peptide is active as an anticoagulant in whole plasma, and is unlikely to elicit an immune response, since it is a normal fibrinolytic cleavage product of this fibrinogen isoform. This application focuses on the development of this peptide as a potential pharmacologic anticoagulant. This peptide anticoagulant would have significant advantages over heparin, and could be used as a general replacement for heparin, particularly when heparin is clinically contraindicated, as in cases of heparin-induced thrombocytopenia. The specific aims are therefore to: I) Express the gamma' chain peptide in a recombinant expression system. II) Assay the recombinant gamma1,' peptide for anticoagulant and anti-platelet activities. At the conclusion of these studies, essential milestones will be achieved for Phase II development of the gamma' peptide as a pharmacologic anticoagulant.